Field of the Invention
This invention relates to the field of gas separation and more specifically to the construction of ultra-thin metal-organic frameworks (MOF), for example zeolitic-imidazolate frameworks (ZIF), for use as gas separation membranes prepared by methods of counter diffusion and ligand/metal exchange.
Background of the Invention
Metal-organic frameworks such as zeolitic-imidazolate frameworks, are a class of organic-inorganic hybrid materials. The metal-organic frameworks are typically crystalline and have metal centers coordinated to organic linkers. Metal-organic frameworks have been found useful for gas separation such as gas separation membrane applications.
Energy efficient membrane-based gas separations are attractive alternatives to conventional separation technologies such as distillation. Despite the great potential of polycrystalline framework membranes (such as MOF membranes) for energy efficient gas separations, the prohibitively high cost of these membranes and processes hampered their practical applications. Amongst other reasons, the high cost may be due to a lack of commercially-viable manufacturing processes and the unsatisfactory membrane performance (e.g., insufficient productivity and selectivity). For membrane applications, metal-organic framework materials are in the form of films on porous supports. Polycrystalline metal-organic framework membranes are made by several different methods. As discussed above, such methods may have drawbacks for industrial applications including the high cost of membranes and membrane production processes as compared to alternatives such as polymeric membranes.
Consequently, there is a need for improved synthesis methods for making membranes and films of metal-organic frameworks that address all of the drawbacks described above.